The present invention relates to methods and apparatus of comminuting rock, coal or other ore-like materials which reduce the capital and operational costs of that comminution. More specifically, the present invention involves the introduction of a liquid into a conical crusher in a manner which increases the production of the crusher, while simultaneously decreasing the cost of subsequent grinding.
Conventional methods of comminution comprise passing raw ore through a series of crushers, screens, and grinding mills until a suitable size of product is produced. The combination of increased capital and operational costs coupled with falling ore grades has forced mine operators to streamline their operations to achieve a lower cost of production per ton of material.
One suggestion for achieving greater milling efficiency involves the collection of the material to be reduced in size, and compressing it between two non-yielding hard surfaces under sufficiently high compression to result in size reduction as well as briquetting of the particles. Preferably the briquettes contain 30-50% of a final product grade material that would be normally obtained as the product of a following grinding/delumping mill. The feed-to-product transformation in such a scheme is claimed to save energy consumption in excess of 10% over the same transformation performed with conventional grinding machinery. The mixing of a suitable liquid with the material before such high compression is stated to result in briquettes of lower strength compared to briquettes formed in the absence of liquid.
This method contains several disadvantages: (1) limited capacity of individual comminution devices (in the range of 20 tons/hour), due to their multi-faceted objective, which includes bringing down the top size, producing 30-50% final product grade material, as well as agglomerating the product into briquettes; (2) briquettes need additional expenditure of energy for delumping; and (3) severe wear of the surfaces effecting the compression of the material to be broken down in size. Traditional high production mining operations require several of such high compression devices, and it is expected that there would not be meaningful cost savings, capital and operating, to implement the technique. Thus, any non-briquetting comminution technique which enhances the productivity of existing, already high capacity crushing and grinding machinery at a substantial savings in overall energy consumption, provides a better, economically feasible approach.
It has been known for some time that crushing in the presence of water will decrease dust, material packing in the crusher chamber and the percentage of fines in the crusher product. Another method of reducing the energy required in the comminution process involves the introduction of water into a crusher to form a slurry containing four percent solids. Tests with a jaw crusher indicate that this wet crushing process provides a 74 percent increase in crushing rate for hard coals and a 121 percent increase for softer coals. In addition, power consumption is reduced by as much as 66 percent compared to conventional dry crushing.
The major disadvantage of this basic wet crushing method is that the extremely low percentage of solids in the slurry is not suitable for large scale commercial milling operations. A later analysis of this method using a cone crusher and slurries of 30 to 60 percent solids revealed that the reduction in required crusher horsepower which followed the introduction of water into the crusher would be essentially offset by the additional power required for supplemental pumps and classifiers needed to practice the process.
Thus, there is a continuing need for an economically feasible method of comminution which requires less energy than conventional systems and requires a reduced level of capital and operational resources.
It is therefore a major object of the present invention to provide an improved method of comminution which results in a reduction of power consumption per ton of ore.
It is another object of the present invention to provide a method of comminution which employs a carrier liquid such as water in the crushing process to achieve a commercially viable reduction in capital and operating costs.
It is a further object of the present invention to provide a method of comminution which results in a greater efficiency in both the crushing and final milling steps.
It is a still further object of the present invention to provide an apparatus which may be used to readily convert conventional cone crushers to crushers capable of water flush crushing.